Showers of heavy isotopes including beryllium-10, are produced when cosmic rays, a high-energy mix of protons, electrons, and atomic nuclei from outside the solar system, collide with molecules in the Earth's atmosphere.

Time scales

By studying beryllium-10 levels in ice cores, scientists can determine the level of solar activity at a given time.

Drawing on two independent ice core records, Owens and colleagues modelled solar activity back to 1610, before the Maunder Minimum.

"Between 1650 to 1710 there were no sunspots recorded, even though there were lots of professional astronomers around at the time," says study lead author Dr Mathew Owens of the University of Reading in the United Kingdom.

"Yet despite the lack of sunspots, the Sun's magnetic field was still churning over its natural eleven-year solar cycle."

"It shows sunspots are a symptom not a cause for the solar cycle."

Magnetic

Sunspots are cooler regions on the Sun's surface caused by magnetic field lines getting twisted as different parts of the Sun rotate at different rates.

As the stresses within the magnetic fields increase, they loop like rubber bands inhibiting convection and causing a decrease in the movement of energy from the Sun's interior.

"This results in a drop in surface temperature, which we call a sunspot," says Owens.

He says, if the activity during solarmax is low the magnetic loops are smaller.

"They're not big enough to generate that cooling, so you don't get sunspots, but you still have the same process going on, just on a different scale."

Owens says the work may be pointing to underlying longer term cycles.

"When we look at previous ice core samples, they show deeper 110-year cycles,

He says this is evident in the number of sunspots seen during this current solarmax, which is the lowest since 1900.

"It's time for the theorists to step up and incorporate these new observations."